This applicaton is related to an application entitled "Method of Driving a Load and Semiconductor Load Driver Circuit Therefor" filed by the same inventors concurrently with this application.
The present invention relates, in general, to semiconductor devices, and more particularly, to circuits for driving loads.
In the past, the semiconductor industry has utilized various circuit configurations to drive loads that are external to the semiconductor device. Inductive and capacitive loads typically require circuitry to compensate for electrical conditions that occur during the termination or initiation of current flow through the load. Of particular interest is circuits that are utilized to drive inductive loads such as ignition coils of internal combustion engines. Often, fault conditions occur during operation of the engines that can cause damage to the semiconductor device driving the ignition coil. For example, a power fault condition can occur when the semiconductor device driving the load remains in the on state for an extended period of time causing high power dissipation within the semiconductor device. This condition can occur during starting of an engine when excessive dwell times may occur. One prior solution is to quickly turn-off the semiconductor device by removing the drive signal when some excessive current level is reached. However, turning-off the semiconductor device can produce a spark that is not properly timed to the engine thereby causing damage to the engine.
Another fault condition that can cause excessive power dissipation within the semiconductor device driving the ignition coil occurs when the ignition coil cannot properly discharge the energy stored within the coil. This can occur during an open secondary or open load condition such as when a spark plug is disconnected or becomes fouled. This type of open secondary or open load condition results in the energy stored within the ignition coil being dissipated within the semiconductor device driving the ignition coil. The excessive energy can damage the semiconductor device. Alternately, the semiconductor device may be made larger in order to handle the excess power, however, this increases the cost of the semiconductor device.
Accordingly, it is desirable to have a semiconductor device and method that can limit or eliminate current supplied to the ignition coil when a power fault condition occurs without producing a spark that would damage the engine, and that can limit power dissipated by the circuit during an open load condition.